Made of solid aluminum. The adaptive buffer tube is Milspec - it is compatible with any Milspec buttstock. The adapter has 8 adjustable positions. Compatible with all markers such as 468, T15, TMC, Milsig, Maxtact, RAP4, Tacamo, Valken M17, CQMF, Milsig M17, M5, MCS100, T16, Wolverine WRAITH X, Redline, PolarStar, Kythera, and Universal ...